PLANETARY-SCALE CIRCULATIONS IN THE PRESENCE OF CLIMATOLOGICAL AND WAVE-INDUCED HEATING

Interaction between the large-scale circulation and the convective pat tern is investigated in a coupled system governed by the linearized pr imitive equations. Convection is represented in terms of two component s of heating: A ''climatological component'' is prescribed stochastica lly to represent convection that is maintained by fixed distributions of land and sea and SST. An ''induced component'' is defined in terms of the column-integrated moisture flux convergence to represent convec tion that is produced through feedback with the circulation. Each comp onent describes the envelope organizing mesoscale convective activity. As SST on the equator is increased, induced heating amplifies in the gravest zonal wavenumbers at eastward frequencies, where positive feed back offsets dissipation. Under barotropic stratification, a critical SST of 29.5-degrees-C results in positive feedback exactly cancelling dissipation in wavenumber 1 for an eastward phase speed of 6 m s-1. Th e neutral disturbance is dominated by Kelvin structure along the equat or and Rossby gyres in the subtropics of each hemisphere. Heating indu ced by the neutral disturbance is magnified in a neighborhood of the e quator, where nearly geostrophic balance in the boundary layer gives w ay to frictional balance. Moisture convergence induced by the Kelvin a nd Rossby structures fuels heating that is positively correlated with the temperature anomaly. Induced heating then generates eddy available potential energy, which offsets dissipation in the neutral disturbanc e. This sympathetic interaction between the circulation and the induce d heating is the basis for ''frictional wave-CISK,'' which is distingu ished from classical wave-CISK by rendering the gravest zonal dimensio ns most unstable. Under baroclinic stratification, the coupled system exhibits similar behavior. The critical SST is only 26.5-degrees-C for conditions representative of equinox, but in excess of 30-degrees-C f or conditions representative of solstice. However, the neutral disturb ance is then no longer confined to the tropical troposphere. Forced by the induced heating, wave activity radiates poleward into extratropic al westerlies and vertically into the stratosphere. Having the form of an unsteady Walker circulation, the disturbance produced by frictiona l wave-CISK compares favorably with the observed life cycle of the Mad den-Julian oscillation (MJO). SST above the critical value produces an amplifying disturbance in which enhanced convection coincides with up per-tropospheric westerlies and is positively correlated with temperat ure and surface convergence. Conversely, SST below the critical value produces a decaying disturbance in which enhanced convection coincides with upper-tropospheric easterlies and is nearly in quadrature with t emperature and surface convergence. The observed convective anomaly, w hich propagates across the Eastern Hemisphere at some 5 m s-1, undergo es a similar shift between amplifying and decaying stages of the MJO. During the same transition, enhanced convection remains phase-locked t o inviscid convergence above the boundary layer, as does induced heati ng in the calculations. Frictional wave-CISK also predicts seasonality in accord with that observed. The coupled system is most unstable und er equinoctial conditions, for which climatological convection and max imum SST neighbor the equator. While sharing essential features with t he MJO in the Eastern Hemisphere, frictional wave-CISK does not explai n observed behavior in the Western Hemisphere, where the convective si gnal is largely absent. Comprised of Kelvin structure with the same fr equency, observed behavior in the Western Hemisphere can be understood as a propagating response that is excited in and radiates away from t he fluctuation of convection in the Eastern Hemisphere.